Update.....

I you don't remove the tranfer case to do the repair like I did, make sure you don't flip the lip of the seal for the output shaft seal for the front diff.

Werewolf,

Not Dville, but I have one that was doing the same thing and under heavy accelleration and loads, there is a loud popping underneath the vehicle that can be felt through the driveline. Pop-pa, Pop, Pop, Pop. You'll thing something is getting ready to come apart hardcore. It's just a nasty sounding noise. If I let the trans kick down at under 30mph I could get it to do it as well, but definitely from a standing start and lunge forward(or attempt to), you'll hear it.